Aspens are trees of the willow family and comprise a section of the poplar genus, Populus sect. Populus. There are six species in the section, one of them atypical, and one hybrid: Populus adenopoda: Chinese Aspen (China, south of P. tremula) Populus sieboldii: Japanese Aspen (Japan) Populus alba: White Poplar (northwest Africa, southern Europe, east to central Asia) Populus × canescens: Grey Poplar (hybrid P. alba × P. tremula) Populus tremula: Common, Swedish, Trembling or E… (More on Aspen)